Capture One can tether (directly) to any Phase One or Leaf digital back regardless of what body they are on. It can not tether to any other brand of digital back.
It can also tether directly to most Canon and Nikon dSLRs. It can also indirectly tether to most other pro cameras via hot-folder, including your M9, though that body does not perform especially quickly as a tethered camera.
Similar backs which would tether to Capture One:
- Phase One P30+H on an H1, H2, or H4X
- Phase One P40+H on an H1, H2, or H4X
- Phase One IQ140H on an H1, H2, or H4X
- Mamiya Leaf Aptus 75s on an H1 or H2
- Mamiya Leaf Aptus-II 8 on an H1 or H2
- Mamiya Leaf Aptus-II 7 on an H1 or H2
- Mamiya Leaf Aptus-II 6 on an H1 or H2
- Mamiya Leaf Credo 40 on an H1, H2, or H4X
Someone else I'm sure (and hope) will answer you more directly about the pros and cons of the back you inquired about.